1. Field of the Invention
The present invention relates to an apparatus for applying heat to a heat-shrinkable plastic film (hereafter referred to simply as "film") to shrink the film into close adhesion with an article wrapped into a package by the film.
2. Description of the Prior Art
A conventional film heat shrinking apparatus of the type described makes use of a hot water shower. The conventional apparatus includes a closed chamber accommodating a hot water tank at its base. Steam is introduced into the hot water tank from outside the chamber to raise the temperature of the water contained in the tank. The hot water so produced is pumped upward from the tank and sprinkled from an overlying shower onto a package wrapped in film and carried into the chamber on a wire screen conveyor. The film wrapping the package is caused to shrink by the heat from the hot water sprinkled thereon. Steam which develops in the closed chamber is discharged through a vent.
The steam is introduced into the hot water tank at a relatively high pressure of 4-5 atm to assure an effective heat exchange between the water and the steam. Steam left after the heat exchange with the water and steam produced by sprinkling the hot water onto the package combine to fill the interior of the closed chamber, thereby raising internal pressure. Since the chamber is provided with entrance and exit openings for the conveyor so that the latter may convey film-wrapped packages in and out, the steam within the chamber is blown out from these openings. The result is a poor working environment in the vicinity of the apparatus. Though the abovementioned duct is provided to discharge much of this steam, heat energy is wastefully discharged along with the steam and the amount of steam consumed is very large.
The hot water shower is also disadvantageous in that the entire surface of the package is not sprinkled with the hot water uniformly, and in that hot water accumulates on the film surface of the package due to a change in the shape of the wrapped package when the film shrinks. The film surface therefore develops a non-uniform temperature distribution so that the film shrinks unevenly. Moreover, the water which has accumulated on the package surface must be removed by post-treatment drying.